In recent years, endoscopic surgery has become the accepted standard for conducting many types of surgical procedures, both in the medical and dental arenas. The availability of imaging devices enabling a surgeon or dentist to view a particular surgical area through a small diameter endoscope which is introduced into small cavities or openings in the body results in much less patient trauma as well as many other advantages.
In many hospitals, the rod lens endoscope is still used in endoscopic surgery. The rod lens endoscope includes a very precise group of lenses in an elongate and rigid tube which are able to accurately transmit an image to a remote camera in line with the lens group. The rod lens endoscope, because of its cost of manufacture, failure rate, and requirement to be housed within a rigid and straight housing, is being increasingly replaced by solid state imaging technology which enables the image sensor to be placed at the distal tip of the investigating device. The three most common solid state image sensors include charged coupled devices (CCD), charge injection devices (CID) and photo diode arrays (PDA). In the mid-1980s complementary metal oxide semiconductors (CMOS) were developed for industrial use. CMOS imaging devices offer improved functionality and simplified system interfacing. Furthermore, many CMOS imagers can be manufactured at a fraction of the cost of other solid state imaging technologies.
One particular advance in CMOS technology has been in the active pixel-type CMOS imagers which consist of randomly accessible pixels with an amplifier at each pixel site. One advantage of active pixel-type imagers is that the amplifier placement results in lower noise levels than CCDs or other solid state imagers. Another major advantage is that these CMOS imagers can be mass produced on standard semiconductor production lines. One particularly notable advance in the area of CMOS imagers including active pixel-type arrays is the CMOS imager described in U.S. Pat. No. 5,471,515 to Fossum, et al. This CMOS imager can incorporate a number of other different electronic controls that are usually found on multiple circuit boards of much larger size. For example, timing circuits, and special functions such as zoom and anti-jitter controls can be placed on the same circuit board containing the CMOS pixel array without significantly increasing the overall size of the host circuit board. Furthermore, this particular CMOS imager requires 100 times less power than a CCD-type imager. In short, the CMOS imager disclosed in Fossum, et al. has enabled the development of a "camera on a chip."
Passive pixel-type CMOS imagers have also been improved so that they too can be used in an imaging device which qualifies as a "camera on a chip." In short, the major difference between passive and active CMOS pixel arrays is that a passive pixel-type imager does not perform signal amplification at each pixel site. One example of a manufacturer which has developed a passive pixel array with performance nearly equal to known active pixel devices and being compatible with the read out circuitry disclosed in the U.S. Pat. No. 5,471,515 is VLSI Vision, Ltd., 1190 Saratoga Avenue, Suite 180, San Jose, Calif. 95129. A further description of this passive pixel device may be found in co-pending application, Ser. No. 08/976,976, entitled "Reduced Area Imaging Devices Incorporated Within Surgical Instruments," and is hereby incorporated by reference.
In addition to the active pixel-type CMOS imager which is disclosed in U.S. Pat. No. 5,471,515, there have been developments in the industry for other solid state imagers which have resulted in the ability to have a "camera on a chip." For example, Suni Microsystems, Inc. of Mountain View, Calif., has developed a CCD/CMOS hybrid which combines the high quality image processing of CCDs with standard CMOS circuitry construction. In short, Suni Microsystems, Inc. has modified the standard CMOS and CCD manufacturing processes to create a hybrid process providing CCD components with their own substrate which is separate from the P well and N well substrates used by the CMOS components. Accordingly, the CCD and CMOS components of the hybrid may reside on different regions of the same chip or wafer. Additionally, this hybrid is able to run on a low power source (5 volts) which is normally not possible on standard CCD imagers which require 10 to 30 volt power supplies. A brief explanation of this CCD/CMOS hybrid can be found in the article entitled "Startup Suni Bets on Integrated Process" found in Electronic News, Jan. 20, 1997 issue. This reference is hereby incorporated by reference for purposes of explaining this particular type of imaging processor.
Another example of a recent development in solid state imaging is the development of a CMOS image sensor which is able to achieve analog to digital conversion on each of the pixels within the pixel array. This type of improved CMOS imager includes transistors at every pixel to provide digital instead of analog output that enable the delivery of decoders and sense amplifiers much like standard memory chips. With this new technology, it may, therefore, be possible to manufacture a true digital "camera on a chip." This CMOS imager has been developed by a Stanford University joint project and is headed by Professor Abbas el-Gamal.
A second approach to creating a CMOS-based digital imaging device includes the use of an over-sample converter at each pixel with a one bit comparator placed at the edge of the pixel array instead of performing all of the analog to digital functions on the pixel. This new design technology has been called MOSAD (multiplexed over sample analog to digital) conversion. The result of this new process is low power usage, along with the capability to achieve enhanced dynamic range, possibly up to 20 bits. This process has been developed by Amain Electronics of Simi Valley, Calif. A brief description of both of the processes developed by Stanford University and Amain Electronics can be found in an article entitled "A/D Conversion Revolution for CMOS Sensor?," September 1998 issue of Advanced Imaging. This reference is also hereby incorporated by reference for purposes of explaining these particular types of imaging processors.
Yet another example of a recent development with respect to sol id state imaging is an imaging device developed by Shell Case, of Jerusalem, Israel. In an article entitled "A CSP Optoelectronic Package for Imaging and Light Detection Applications" (A. Badihi), Shell Case introduces a die-sized, ultrathin optoelectronic package which is completely packaged at the wafer level using semiconductor processing. In short, Shell Case provides a chip scale package (CSP) process for accepting digital image sensors which may be used, for example, in miniature cameras. The die-sized, ultrathin package is produced through a wafer level process which utilizes optically clear materials and completely encases the imager die. This packaging method, ideally suited for optoelectronic devices, results in superior optical performance and form factor not available by traditional image sensors. This reference is also incorporated by reference for purposes of explaining Shell Case's chip scale package process.
Yet another example of a recent development with respect to solid state imaging is shown in U.S. Pat. No. 6,020,581 entitled "Solid State CMOS Imager Using Silicon On Insulator or Bulk Silicon." This patent discloses an image sensor incorporating a plurality of detector cells arranged in an array wherein each detector cell has a MOSFET with a floating body and operable as a lateral bipolar transistor to amplify charge collected by the floating body. This reference overcomes problems of insufficient charge being collected in detector cells formed on silicon on insulator (SOI) substrates due to silicon thickness and will also work in bulk silicon embodiments.
The above-mentioned developments in solid state imaging technology have shown that "camera on a chip" devices will continue to be enhanced not only in terms of the quality of imaging which may be achieved, but also in the specific construction of the devices which may be manufactured by new breakthrough processes.
Although the "camera on a chip" concept is one which has great merit for application in many industrial areas, a need still exists for a reduced area imaging device which can be used in even the smallest type of endoscopic instruments in order to view areas in the body that are particularly difficult to access, and to further minimize patient trauma by an even smaller diameter invasive instrument.
It is one object of this invention to provide reduced area imaging devices which take advantage of "camera on a chip" technology, but rearrange the circuitry in a stacked relationship so that there is a minimum profile presented when used within a surgical instrument or other investigative device. It is another object of this invention to provide low cost imaging devices which may be "disposable." It is yet another object of this invention to provide reduced area imaging devices which may be used in conjunction with standard endoscopes by placing the imaging device through channels which normally receive other surgical devices, or receive liquids or gases for flushing a surgical area. It is yet another object of this invention to provide a surgical device with imaging capability which may be battery powered and only requires one conductor for transmitting a pre-video signal to video processing circuitry within or outside the sterile field of the surgical area.
In addition to the intended use of the foregoing invention with respect to surgical procedures conducted by medical doctors, it is also contemplated that the invention described herein has great utility with respect to oral surgery and general dental procedures wherein a very small imaging device can be used to provide an image of particularly difficult to access locations. Additionally, while the foregoing invention has application with respect to the medical and dental fields, it will also be appreciated by those skilled in the art that the small size of the imaging device set forth herein can be applied to other functional disciplines wherein the imaging device can be used to view difficult to access locations for industrial equipment and the like. Therefore, the imaging device of this invention could be used to replace many industrial boroscopes.
The "camera on a chip" technology can be furthered improved with respect to reducing its profile area and incorporating such a reduced area imaging device into very small investigative instruments which can be used in the medical, dental, or other industrial fields.
Because of the sophisticated optics and circuitry contained in modern endoscopes, they can be very expensive and difficult to maintain. Additionally, since the size of the endoscope is still a major concern in endoscopic procedures, standard surgical instruments must be modified to reduce their size in order that the instruments can be used simultaneously with the endoscope. For example, it is well-known in the art to provide a plurality of channels within or around the endoscope in order that miniature surgical instruments such as forceps or the like may be simultaneously introduced with the endoscope. Therefore, the construction of most prior art endoscopes begins first with consideration of the size of the endoscope, and then operative channels are formed within or around the endoscope so that the modified surgical instrument may be introduced simultaneously to the site under investigation.
Although great advances have been made in the electronic industry in terms of reducing the size of the imaging elements which are used within the endoscope, many endoscopes in use continue to be too large to conduct certain surgical procedures. Additionally, many surgical procedures cannot be effectively conducted with the miniaturized surgical instruments. Rather, a more full size surgical instrument is still required. Furthermore, cost continues to be a prohibitive factor because the special surgical instruments must be manufactured which are small enough to fit within the small channels of the endoscope being used.
From the foregoing, it is apparent that an even smaller imaging device is desirable which can be used universally with larger and more standard sized surgical instruments in order to reduce the cost of providing endoscopic capability for certain surgical procedures as well as maintaining a minimally invasive sized instrument with imaging capability which is used to conduct such surgical procedures. Accordingly, the imaging device of this invention is ideally suited to overcome the shortcomings of most modern endoscopes discussed above.